1. Field of the Invention
The present invention relates to household appliances, and more particularly to cooling systems such as those utilized in refrigerators, freezers and air conditioners.
2. Background Art
In the usual operation of appliances, such as refrigerators, freezers and even air conditioners, ice may build up on the evaporator included within the refrigeration system due to moisture in the air. Such ice build up reduces the efficiency of the system and decreases food preservation time because any act of defrosting causes warming of the air in contact with the melting ice.
In the past, a number of different ways have been utilized to determine the need for defrosting of the appliances. The usual techniques include various sensors on the evaporator to measure for ice presence. Some defrost methods are based purely on total time or run time of the compressor. Others frequently include combinations of the number of door openings, while still others employ a technique of recording how long a previous defrost in the appliance took by sensing the switch and comparing this to an optimum time that the switch should be operated. Such methods typically utilize the sensing of the operation of a bi-metallic switch.
A search of the background art directed to the subject matter of the present invention conducted in the U.S. Patent and Trademark Office disclosed the following U.S. Letters Patent:
U.S. Pat. No. 4,689,965 pertains to a control used in conjunction with a refrigeration system that includes defrosting apparatus for removing a frost load from the evaporator and means for energizing the defrosting apparatus at the end of a cooling cycle to initiate a defrost cycle.
U.S. Pat. No. 5,251,454 teaches the control of a defrost cycle of a refrigerator by placing a thermistor between the fins of the included evaporator. Comparator circuitry compares the temperature between that and a set point within the refrigerator.
U.S. Pat. No. 4,407,138 pertains to a control system for initiating the frost mode of operation in a heat pump wherein the ambient temperature is continuously monitored along with various other temperatures to determine appropriate control.
U.S. Pat. No. 5,257,506 pertains to a method for controlling a defrost cycle for effecting the defrost of an outdoor heat exchanger coil by initiating a defrost cycle as a function of outdoor coil temperature and outdoor air temperature.
U.S. Pat. No. 5,319,943 pertains to a microprocessor based control system for controlling frost accumulated on the outdoor evaporator coil of a heat pump.
U.S. Pat. No. 4,974,417 and 4,974,418 deal again with heat pump defrosting operations. These patents teach microprocessor control and the inclusion of exterior temperature sensors.
Based on a thorough review of the above-identified patents, we believe that none of the above teach, disclose or claim the novel combination of elements and functions found in the improved cooling system taught by the present invention.